The resonant converter, especially LLC resonant converters, have been widely used as a DC-DC converters due to its high efficiency and hold-up capability. However, the control characteristics of the resonant converters are much more complex compared to PWM converters due to the dynamics of the resonant tank. Optimal Trajectory Control (OTC) was first proposed to control Series Resonant Converter (SRC). Then state-trajectory analysis and control were employed to solve the challenges in the control of the LLC resonant converter. These state-trajectory control methods are based on resonant tank information.